A hybrid vehicle is driven by combining two different power sources, for example, an engine torque by combusting fuel (fossil fuel such as gasoline) and a motor torque by battery power.
The hybrid vehicle uses an engine and an electric motor as an auxiliary power source to reduce exhaust gas and enhance fuel efficiency. Studies on the hybrid vehicle have been actively conducted to meet the demands of enhancing fuel efficiency and developing environmentally-friendly products.
The hybrid vehicle generally uses a motor having relatively low-speed torque characteristics at a low speed as a main power source and uses an engine having relatively high-speed torque characteristics at a high speed as a main power source.
Therefore, the hybrid vehicle stops the engine at a low speed section and operates the motor, and therefore improving fuel efficiency and reducing exhaust gas.
FIG. 1 is a diagram illustrating an example of a hybrid power-train according to the related art, which includes an engine 1, a first motor MG1, and a second motor MG2.
The first motor MG1 serves as a generator which generates power by a driving force of an engine 1, and the second motor is directly connected to an output shaft 4 to implement an electric vehicle (EV) mode.
An input shaft 2 which is connected to the engine 1 is provided with an over drive clutch 3. The over drive clutch 3 directly connects the input shaft 2 to the output shaft 4 to implement a high efficiency point operation of an engine at the time of the high speed driving of the vehicle and is in a released operation state at normal times.
According to the related art, since the second motor MG2 is connected to the output shaft 4 via two pairs of gears, efficiency of the EV mode is increased, and thus, fuel efficiency of plug-in hybrid electric vehicle charge depleting (PHEV CD) is excellent.
However, as all the driving forces of the engine at the time of driving a vehicle in a hybrid electric vehicle (HEV) mode are transferred to the first motor MG1 and are output via the second motor (MG2) after the first motor MG1 generates power, conversion losses of mechanical energy and electrical energy occur, and therefore, the fuel efficiency of plug-in hybrid electric vehicle charge sustaining (PHEV CS) significantly decreases. Further, since the two motors MG1 and MG2 are used, the hybrid power-train according to the related art is expensive.
FIG. 2 is a diagram illustrating another example of a hybrid power-train according to the related art, which includes an engine 1, first and second planetary gear sets PG1 and PG2, a first motor MG1, and a second motor MG2.
The first motor MG1 as a generator is connected to the input shaft 2 of the engine 1 through the first planetary gear set PG1 to receive a driving force of the engine 1.
The second motor MG2 is directly connected to the output shaft 4 through the second planetary gear set PG2 and a pair of gears to implement the EV mode.
According to the related art of another example as described above, the driving force is transferred via the planetary gear set PG1 and the two pairs of gear at the time of EV driving. Thus, transfer efficiency is relatively reduced and the driving force of the engine is branched through the planetary gear set PG2, and therefore, the energy conversion loss is reduced. However, a power generation operation is performed by using the first motor MG1 and therefore the efficiency thereof is low. Further, since two motors such as the first and second motors MG1 and MG2 are used, the hybrid power-train according to the related art is expensive.